General directories are a good starting place when you have a general question.
Their content is (usually) handpicked by humans - "Is this site of enough interest to enough people that it should be included in a directory?"  (money helps)
If the answer is "Yes", then it is added to the directories database and placed in one or more of the subject categories.
As a result sites in directories are selective and categorised.

Strengths Selective Classified Easily browsed Good for general questions Most have some searchability

Weaknesses Small database May not be specific Paid inclusion may affect quality Tend to index only the main page